1. Field of the Invention
The present invention relates to a beam analyzing system and a method for analyzing pulsed particle or laser beams.
2. Discussion of Prior Art
In accelerator machines in which a pulsed beam (particle or laser beam) is used the exact determination of the position of a beam pulse in time and space as well as the determination of the energy of the beam pulses is of major importance. For example, in a free electron laser a pulsed electron beam is used to generate pulses of coherent light in a so-called undulator installed at the end of the course of beam. For this purpose the electron beam is steered on a sinusoidal path in the undulator by magnetic fields, such that coherent light is emitted into the forward direction of the electron beam. By virtue of the pulsed electron beam this coherent light is also pulsed.
In experiments with free electron lasers these pulsed characteristics are for example used to conduct measurements of ex-cited states of atoms or molecules, wherein the excited states are initially generated by a pulse of an excitation laser. In experiments of this kind the time between the excitation pulse on the one hand and the pulse of the free electron laser on the other hand is selectively varied to thereby determine properties of excited states, such as decay times.
It results from this that it is of major importance for experiments of this kind to know the exact timing of the beam pulses relative to a pulsed reference signal, wherein a pulsed laser beam may be used as reference signal.
In the following, this timing is referred to as “phasing” of the beam pulses.
Moreover, the spatial position of the particle beam is also of interest as in certain sections of the accelerator a variation of the transverse position corresponds to a variation in energy. An exact determination of the energy of the particle beam can therefore in those sections be accomplished by a precise measurement of the transverse position of the particle beam.
From the prior art it is known to use an antenna in a beam pipe section for the determination of the timing of the particle beam. By means of the beam pulse a voltage pulse is induced in the antenna and e.g. conducted through a band pass filter and amplified afterwards. The amplified signal is mixed with a reference signal in an HF-mixer to a lower frequency. The phase information is then extracted from the low-frequency signal.
It is disadvantageous about a system of this kind that the mixed output signal is inter alia affected by variations of the frequency or the phase of the reference signal, thus a drift appearing in the reference signal leads to the output signal varying independently from the timing of the beam pulse. Due to the fact that just a small frequency band of the electrode signal is analyzed the signal levels are in addition low, which limits the resolution of this method.
For the measurement of the arrival time of laser beam pulses a method for determining the cross-relations between a reference laser beam and a laser beam to be analyzed by means of a frequency-doubling crystal is known from the prior art. However, it is a major disadvantage that there is not a suitable crystal for any combination of a reference laser with a laser beam to be analyzed available, e.g. in the UV-domain or at too low power outputs.